Biosensors are measuring instruments that examine the properties of a substance using functions of an organism. These biosensors are excellent in sensitivity and reaction specificity because the biosensors use a biomaterial as detecting element. Thus, the biosensors are broadly used in various fields such as clinical chemical analysis, process instrumentation of bioindustry, environment instrumentation, stability evaluation of chemicals, and so on, and their usage is continuing to spread. Particularly, a variety of biosensors are used in a medical diagnostic field to analyze samples, particularly bio-samples. The biosensors are divided into enzyme assay biosensors and immunoassay biosensors according to the kind of detecting element, and into optical biosensors and electrochemical biosensors according to a method of quantitatively analyzing a target substance within a bio-sample.
The enzyme assay biosensors are designed to use a specific reaction between an enzyme and a substrate and a specific reaction between an enzyme and an enzyme inhibitor, and the immunoassay biosensors are designed to use a specific reaction between an antigen and an antibody.
The optical biosensors are widely used to measure a concentration of a target material by measuring transmittance, absorbance, or alteration in wavelength. The optical biosensors have an advantage in that, since reaction mechanisms of various materials to be analyzed have already been known and measurement is made after a reaction takes place for a sufficient time, a deviation in measurement time is low. In contrast, the optical biosensors have a disadvantage in that they require a longer measurement time and a greater quantity of samples than the electrochemical biosensors. Further, the optical biosensors have other disadvantages in that measured results are influenced by turbidity of a sample, and it is difficult to miniaturize an optical unit.
The electrochemical biosensors are used to measure a concentration of a target material by measuring an electric signal obtained from a reaction. The electrochemical biosensors have advantages in that it is possible to amplify a signal using a very small quantity of sample, they are easy to miniaturize, it is possible to stably obtain a measured signal, and they can be easily combined with a telecommunication instrument. However, the electrochemical biosensors have disadvantages in that an electrode manufacturing process is additionally required, the cost of production is high, and a measured signal is very sensitive to response time.
Meanwhile, a capillary structure is typically used to introduce a biomaterial such as a sample into a measuring region of the biosensor. In the case of conventional biosensors using such a capillary structure, a vent hole is generally formed in some of substrates forming a capillary. This vent hole allows air in the capillary to be discharged to the outside while a bio-sample is introduced into the capillary of the biosensor, thereby forcing the bio-sample to be continuously introduced into the capillary.
A biosensor having an opposing electrode structure is disclosed in U.S. Pat. No. 5,437,999. In this biosensor, three substrates including spacer are adhered to form a capillary gap, and upper and lower substrates are each provided with a vent hole at the same position. Thus, when a sample is introduced into the capillary gap defined by the three substrates including the spacer, air in the capillary gap is discharged to the outside via the vent holes formed in the upper and lower substrates. Another biosensor is disclosed in U.S. Pat. No. 5,759,364, in which several substrates including an embossed substrate are adhered to form a capillary gap. In the biosensor, the uppermost substrate is provided with a vent hole to discharge air in the capillary gap when a sample is introduced.
In the case of these conventional biosensors, the capillary gap is formed by deforming or processing the substrate, so that the manufacturing process is complicated and expensive. Further, when the sample is introduced into the capillary gap, the air in the capillary gap is pushed out only through the vent hole, and thus the sample is introduced at a low speed. In addition, when a capillary wall has high friction, the sample may be introduced at a lower speed.